Compositions according to the present disclosure may be useful in a variety of lubricating and power transmitting applications, for example, in automatic transmissions, such as, continuously variable transmitting applications and/or automated manual transmissions, with or without start-up devices, such as torque converters.
There has been a steady growth in the number of automobile manufacturers using or planning to use continuously variable transmissions (CVTs) in place of conventional automatic transmissions. CVTs have been shown to impart improved fuel efficiency and driving performance as well as reduced emissions compared to conventional automatic transmissions.
CVTs may contain a steel push-belt and pulley assembly, a chain and pulley assembly, or a disk assembly (in the case of toroidal CVTs), in combination with a torque converter or some other form of a start-up device. Torque is transmitted through metal-metal contact between the pulley and the belt or chain or disk. Efficient transmission of torque requires relatively high steel-on-steel friction with minimal wear between the belt or chain and the pulley. Low friction can lead to belt slippage or catastrophic wear. Steel-on-steel friction is therefore a critical requirement for transmission of torque. The additive technology employed to raise steel-on-steel friction may lead to higher steel-on-paper friction. In CVT assemblies with torque converters as the start-up device, the presence of the torque converter clutch requires that CVT fluids have an appropriate level of steel-on-paper friction in order to avoid problems that plague transmission fluids with high friction. An example of such a problem is shudder. CVT starting clutches must provide the same functions as those in conventional automatic transmissions in addition to needing to meet the requirements for the CVT. Thus, one of the principal challenges to a formulator developing CVT fluids is balancing steel-on-steel friction requirements with those for steel-on-paper friction.